I am working on 1-D simulation of matric suction (negative pore water pressure) in unsaturated expansive soils using Richard's equation (similar to equation 2.1 in the Hydrus handout: HYDRUS1D-4.08). The difference in simulating matric suction of expansive soils versus non-expansive soils is that volume change has to be considered in the simulation of expansive soils. Therefore, gravimetric water-content-SWCC must be performed, and additional geotechnical lab tests must be done. As a result, a set of additional parameters will be introduced to the unsaturated hydraulic conductivity function (equation 2.2 in the Hydrus handout: HYDRUS1D-4.08).
My question is: can I modify the unsaturated hydraulic conductivity function to include these geotechnical parameters?
Note: the unsaturated hydraulic conductivity function I am trying to use will still make the PDE non-linear and will be in terms of i) matric suction, ii) shrinkage curve (void ratio versus gravimetric water content) parameters, iii) saturated hydraulic conductivity versus void ratio parameters, and iv) true air entry value (air entry suction) in terms of degree of saturation. Also, the unsaturated hydraulic conductivity function will still be a product of the relative hydraulic conductivity and the saturated hydraulic conductivity.
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You certainly can do it. The source code of the HYDRUS-1D computational module is on the HYDRUS website. All calculations related to soil hydraulic properties are done in the functions grouped in the Material.for file. J.